1. Field of the Invention
The invention relates to an apparatus for performing actuations or operations in a printing press.
By the term actuations or operations there is meant, for example, switching or controlling, coupling, adjusting and tensioning operations, wherein machine or press parts are moved and/or held in a given position. Such actuations may be necessary in various devices of the printing press, a defined sequence of actuations having to be adhered to, depending upon the functions of the individual devices and to assure disruption-free cooperation of the devices. The actuations often require a transmission of comparatively strong forces to devices located at various places in the printing press which in terms of structural space are quite restricted. Pneumatic and hydraulic systems are therefore used for these purposes.
In the published German Patent Document DE 44 01 684 A1 and U.S. Pat. No. 5,588,363, a method for performing successive work steps in a printing press by the application of a pressure medium in various pressure stages upon actuators preloaded in the opposite direction is proposed. Also proposed therein is an apparatus for performing the foregoing method which has a piston-cylinder unit with a differential piston. One piston face of the differential piston can be subjected in a cylinder chamber to a pressure medium of a first pressure medium system with a pressure stage regulation, and another piston face acts in another cylinder chamber on a pressure medium of a second pressure medium system which, in turn, acts upon the actuators.
An unfavorable aspect of this heretofore known method and device is that, in addition to the piston-cylinder unit, pressure stage regulation is required, for example, in the form of a switchable or controllable pressure regulator or pressure limiter, which is all the more complicated, the greater the number of work steps that have to be performed in succession. Another disadvantage is that the piston-cylinder unit produces relatively little output power relative to the structural size thereof, that is, if a low pressure is applied to the cylinder input side, a high pressure on the cylinder output side cannot be generated by the pressure conversion performed there. The preloading magnitude of the actuator which is preloaded with a maximal force can therefore be only comparatively slight, especially if the actuators are intended to be of small structural dimensions. On the one hand, actuations to be performed with great force, such as fastening cylinder coverings, can be achieved only at the cost of the disadvantage of a piston-cylinder unit with a large piston face that occupies a great deal of space in the radial direction. On the other hand, this complicates the adaptation to one another of the forces that preload the actuators and in terms of the pressure stage regulation, especially when a great number of switching operations on the part of the adjusting cylinders must be performed successively. Because there is only a slight difference between the minimal and maximal preloading of the adjusting cylinders, only a limited number of adjusting cylinders can be switched or controlled in succession, because assurance must be provided that any partial relief of the adjusting cylinders of a higher pressure stage is so slight that a switching operation cannot yet take place when the switching of the adjusting cylinders of a lower pressure stage is already occurring.
In the German Patent Document DE 39 25 110 A1, a cylinder of the tandem cylinder type is proposed which produces increased power without any increase in the dimensions or operating pressure thereof. The tandem cylinder is formed of a housing with openings acting alternatively as inlets or outlets for the pressure fluid, a central column; and a member in the form of an inverted beaker. The housing forms a first expansion chamber wherein a piston with a first annular, pressure-absorbing face reciprocates. The column extends upwardly from the bottom of the housing, the piston being disposed on the open end of the member. The inner surface of the cap of the member acts as a second pressure-absorbing face, and the interior of the member acts as a second expansion chamber.
An unfavorable aspect thereof is that, with this tandem cylinder, only two pressure stages can be achieved, and the construction principle of the tandem cylinder, which is formed of individual parts that are complicated to produce, entails a major production expense.
The brochure entitled "Leibfried Antriebseinheiten Anlagentechnik Schrift ("Leibfried Drive Units Installation Technology") 7501175.05.03.093" published by the firm Leibfried Maschinenbau GmbH discloses a compressed air cylinder, type LMZT, of the tandem construction type in a bidirectional version. This tandem cylinder has two conventional piston-cylinder units disposed in alignment with one another in the axial direction of the cylinders, which form a common housing encompassing two expansion chambers that are subjectible to the application of pressure. One adjusting piston is disposed in each expansion chamber, and one adjusting piston rod, when pressure is imposed on the adjusting piston disposed thereon, acts to transmit force to the other adjusting piston rod. When pressure is imposed simultaneously in both expansion chambers, an increased output of power is achieved, and installation of the tandem cylinder in an apparatus in the radial direction requires only little installation space.
This tandem cylinder has the same disadvantages as those of the type of tandem cylinder described hereinbefore with respect to the aforementioned published German Patent Document DE 39 25 110 A1.